1. Field of the Invention
The present invention is directed to a spatial light modulator and, more specifically, to a spatial light modulator with improved inter-pixel performance.
2. Technical Background
Reflective liquid crystal (LC) spatial light modulators (SLMs) have been constructed with spatially distributed discrete pixels in one or more dimensions. FIG. 1 depicts a partial cross-section of a typical prior art SLM 100, absent a number of common barrier layers, such as silicon nitride (SiN) and silicon dioxide (SiO2), which are well known and not particularly relevant to the present discussion and therefore are not illustrated. As is shown in FIG. 1, the SLM 100 includes a transparent first substrate 102, which includes a continuous optically transparent first electrode 106, formed on an upper surface of the substrate 102, that serves as a ground electrode. A top and second substrate 104 includes a pixel layer 108 formed on a lower surface, which includes a number of discrete conductive pixel elements 108A, 108B and 108C. A transparent alignment layer 112 is formed over the layer 108 and a transparent alignment layer 116 is formed over the first electrode 106. The alignment layers 112 and 116 may be made of a polyamide and are used to align LC molecules of electro-optic material 114.
The pixel elements 108A-108C also function as mirrors and act to reflect an incoming light beam that travels through the electro-optic material 114, e.g., a liquid crystal (LC) film, interposed between the layer 108 and the electrode 106, when a potential difference applied between one of the pixel elements 108A-108C and the first electrode 106 is such that the electro-optic material 114 in the area of at least one of the pixel elements 108A-108C is transmissive.
The pixel element 108A is separated from the pixel element 108B by an inter-pixel region 110A and the pixel element 108B is separated from the pixel element 108C by an inter-pixel region 110B. With reference to a center of the pixel element 108B, it will be appreciated that due to electrical field fringing and the absence of an electrode material, the optical properties (e.g., insertion loss) of the inter-pixel regions 110A and 110B will differ from that of the center of the pixel element 108B. FIG. 2 depicts a graph illustrating a typical insertion loss associated with the SLM 100 of FIG. 1. As shown in FIG. 2, the insertion loss attains a maximum loss at points 120 and 122, which correspond to inter-pixel regions 110B and 110A, respectively. As is also illustrated at points 124, 126 and 128, the respective insertion losses associated with the pixel elements 108A, 108B and 108C is less than the insertion loss associated with the inter-pixel regions 110A and 110B.
In many applications, the difference in the optical properties between a center of a pixel element and an inter-pixel region is not critical and inter-pixels regions can simply be masked with an absorbing material. However, in a number of applications, it is desirable for the inter-pixel regions to have optical properties, which are similar to that of the pixel element centers. For example, when channels are banded to produce a continuous spectrum it is desirable for the inter-pixel regions of an SLM to have the same characteristics as the pixel element centers.
Thus, a spatial light modulator (SLM) whose inter-pixel regions have optical properties that are substantially similar to the optical properties of pixel element centers is desired.
One embodiment of the present invention is directed to a reflective spatial light modulator (SLM) that includes a first substrate, a second substrate and an electro-optic material positioned between the first and second substrates. According to one embodiment, the first substrate includes a continuous reflective ground layer that acts as a first electrode and the second substrate is transparent and includes a pixel layer having a plurality of pixel elements formed in a pattern. The pixel elements are formed of a transparent conductive material and are separated by inter-pixel regions formed of a non-conductive material. A transmissivity of the electro-optic material in a vicinity of each of the plurality of pixel elements is controlled by a potential difference applied between the first electrode and a respective one of the pixel elements.
According to another embodiment of the present invention, a reflective SLM includes an optically transparent first substrate, a second substrate, an electro-optic material positioned between the first and second substrates and a dielectric mirror. The first substrate includes a ground layer that acts as a continuous transparent first electrode. The second substrate includes a pixel layer having a plurality of pixel elements formed in a pattern. The pixel elements are formed of a conductive material and are separated by inter-pixel regions formed of a non-conductive material. The transmissivity of the electro-optic material in a vicinity of each of the plurality of pixel elements is controlled by a potential difference applied between the first electrode and a respective one of the pixel elements. The dielectric mirror is positioned between the pixel layer and the electro-optic material.
Additional features and advantages of the invention will be set forth in the detailed description which follows and will be apparent to those skilled in the art from the description or recognized by practicing the invention as described in the description which follows together with the claims and appended drawings.